At $45 And Up, We Reach For Power Supply Gold
Part one of our budget power supply round-up debated the merits of four PSUs ranging from 350 to 550 W, all of them flashing 80 PLUS Bronze ratings. Aside from the Cougar A350, all of them proved capable of satisfying the specification. Today we're looking at four more power supplies, this time ranging from 360 to 550 W. The range is a little narrower, but the contenders are all still quite comparable. Three sport the same Bronze logo, but one, Seasonic's SSR-360GP, boldly claims compliance with 80 PLUS' Gold standard, typically reserved for $100-plus products. All the while, the SSR-360GP sells for a mere $60.
Although that aggressive price gets our attention, we aren't going to neglect the other three test candidates: Cooler Master's Silent Pro M2 520W, Corsair's CX500, and Gigabyte's Greenmax Plus 450W. That Gigabyte unit doesn't seem to be available in the U.S., but with 550 W and 650 W versions showing up on Newegg, we're hoping to see the 450 W model soon.
As with yesterday's story, we again asses the sound levels of each PSU. This is something readers have been requesting for a while. Until now, though, we lacked a practical and reproducible methodology. From now on, we'll be measuring acoustics at three load levels: 40 W, which simulates an idle PC or a machine running office applications; 200 W, standing in for a mid-range gaming workload; and a 600 W draw to replicate what a more extreme gaming PC might encounter with a couple of graphics cards installed. That should get each unit's cooling fan spinning as fast as possible. Of course, if 600 W exceeds the maximum output of a power supply, we made do without it and simply use the other two.
In order to simulate these loads, we built a test fixture consisting of 12 V/40 W light bulbs, which imposes a purely resistive load on the power supply. With 15 lights, we can simulate any load between 40 W and 600 W, in 40 W steps. We are aware of the fact that a purely resistive load may stress a power supply differently than the partly capacitive, partly inductive load of a real-world PC. But we’re not overly worried; this synthetic load should be perfectly suited for measuring the sound level of the PSUs at each load level. Acoustics are measured one foot away from each power supply's fan, and we let each unit settle for half an hour any time we change the load.
Note that, in part one, we talked about a unique anomaly exhibited by one of our instruments. In short, after we upgraded oscilloscope probes to better ones, all of the PSUs we tested started showing spikes that the previous, less expensive probes never displayed. After some back-and-forth with a couple of power supply vendors, we came to the conclusion that our new probes allow us to pick up short spikes that the old ones missed.
